A University of Sussex PhD thesis Available online via Sussex Research Online: http://sro.sussex.ac.uk/ This thesis is protected by copyright which belongs to the author. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Please visit Sussex Research Online for more information and further details Tracing star formation and AGN activity at radio frequencies Dániel Csaba Molnár Submitted for the degree of Doctor of Philosophy University of Sussex May 2018 Declaration I hereby declare that this thesis has not been and will not be submitted in whole or in part to another University for the award of any other degree. This thesis is written in the paper based style, as approved by the University. Chapter2 was published in Further evidence for a quasar-driven jet impacting its neighbour galaxy: The saga of HE0450-2958 continues, Molnár et al., 2017, Monthly Notices of the Royal Astronomical Society, Volume 467, Issue 1, p.586-596. I contributed to all aspects of this paper, with other authors giving comments, advice and helped in some aspects of the analysis. Chapter3 was published in The infrared-radio correlation of spheroid- and disc-dominated star-forming galaxies to z ∼ 1.5 in the COSMOS field, Molnár et al., 2018, Monthly Notices of the Royal Astronomical Society, Volume 475, Issue 1, p.827-838. I contributed to all aspects of this paper, with other authors giving comments, helped in some aspects of the analysis and provided access to data. Signature: Dániel Csaba Molnár iii UNIVERSITY OF SUSSEX Dániel Csaba Molnár, Doctor of Philosophy Tracing star formation and AGN activity at radio frequencies Summary My research has focused on locating and measuring star formation and AGN activity in different environments with interferometric and single-dish radio observations. As my first PhD project, I studied the complex interaction between an intermediate redshift (z ∼ 0.3) starburst galaxy and a nearby (∼ 7 kpc separation) QSO using sub-arcsecond VLA observations. I found new evidence for jet-induced star formation activity in the companion galaxy, making the system a strong candidate for this rare, and potentially important process in the early Universe. In my second paper, I investigated the infrared-radio correlation (IRRC) of spheroid- and disc-dominated galaxies in the COSMOS field out to z ∼ 1.5. With 1.4 GHz data and Herschel photometry I found that the redshift evolution reported in recent works is due to an increasing radio excess emission associated with spheroid-dominated galaxies, compared to disc-dominated ones, i.e. the ‘purest’ star-forming systems in our sample. I theorize that the extra radio power in spheroid-dominated systems is due to low-level AGN activity, even though these sources were not identified by most commonly-used diagnostics as AGN hosts. This finding will significantly increase the accuracy of future high-redshift radio surveys measuring star formation. In my third project I assembled and analysed the largest-to-date low-z IRRC sample of galaxies. I demonstrated the importance of selection effects influencing IRRC statistics, and carried out an improved IRRC analysis that yielded more accurate measures of the correlation’s properties. With rich ancillary data it will provide insight into the physical processes that give rise to the IRRC. Finally, I adopted an MCMC-based model optimization to fit a radiative transfer model to ammonia line spectra of a binary molecular cloud core. I determined the physical structures and the masses of the cores and found they are gravitationally unbound. iv Acknowledgements Ezt a dolgozatot édesanyámnak, és eltávozott nagyszüleimnek, Teri mamának, Jenő papának és Árpi papának ajánlom. Hiányoztok nagyon, de remélem jól érzitek magatokat fényév távolsagra innen! Igyekszem gyakran arra nézni. This thesis is dedicated to my mother, and my grandparents who passed away, Teri mama, Jenő papa and Árpi papa. I miss you a lot, but I hope you’re having a good time light-years away from here! I often try to look your way. First and foremost I owe the largest and most sincere thanks to my supervisor, Mark Sargent! He kept me motivated and guided me tirelessly with great empathy and patience, and I cannot be grateful enough for all the effort (far beyond what is usual) he put into mentoring me. I thank my ‘temporary supervisors’ and hosts in Zagreb and Heidelberg, Vernesa Smolčić and Eva Schinnerer, for providing me the awesome opportunity to join their teams and their excellent support for the rest of my PhD. My thanks to the entire VLA-COSMOS team and all my further collaborators named in the following pages for their great feedback that contributed in many many ways to this thesis. I also acknowledge support from the Science and Technology Facilities Council (grant number ST/M503836/1). All the amazing friends I made in the past few years – you turned moving across the Channel to a strange new land into an exciting and fun journey. Special thanks go to my THOA housemates, who became my family-in-another-country. Alex for all those times he pulled the wrong token from the chaos bag; my lil’ bro, Benoît, for standing by me since day one; Heena for patiently putting up with us; Ridwan, for every hearty laugh and also the quiet moments; and of course for THOA v2: Panka for the constant stream of treats from home; and Jacob for liking every single film we have seen together. The staff and PhD community in the Astronomy Centre is exceptional. I am especially grateful to my officemates; Steve for being our all-time pubmeister, Charlotte and Antonio for welcoming me warmly (back in the ancient times), Sean for inspiring me to maybe, hopefully one day go back to running, and Michaela for that one time she brought Charlie in. My ‘cosmic’ nemeses Zé and Ana, the always-laughing Lucía, my late-dinner-mate Hannah, komrads Sunayana and Mateja, v Azizah, who kept me ‘humble’, Rose, my radio buddy, friend Ciaran and all the great people in the astro corridor receive massive thanks too. Last but not least, I want to say cheers to the legendary and respectful Dr. Scott ‘Bestie’ Clay and Dr. David ‘FacebookUser’ Sullivan for the top bants. I owe a great deal of gratitude to the people who supported me during my extended visits. The Zagreb crew: Lana (potato!), Olga, Ivan, Mladen, Oskari, Nicola and Dinko. I still wear the sports department t-shirt! Special thanks go to Jacinta, who talked me through some very critical moments. I would also like to thank my dear friends in Heidelberg: Sarah for the irregular but lovely coffee breaks and Philipp for being my travelling room mate. I am grateful to Saci for listening to my complaints even from the other end of the world. B811 – Gábor, István and Karesz. Thank you for the endless memes! Extended-B811 – Dia, thanks for letting us in your flat despite all the Klein bottles of the world coming with us, and thank you, Anna, for letting me become part of your family! I also thank the entire Szántód team (Dani & Kati, Pite, Ádám, Rita, Viki, Csibe, Nóri, Gyuri & Zsófi, KZD and Kálmán bá) for the annual summer retreats and your undying friendship. Here’s to another 10 years and more! Orsi, thank you for the burger breaks! Hugs to my token non-astro friend, Laura. Thanks to Száva and Anita for making me want to migrate to Zürich. And finally, but most importantly, I want to express my love and gratitude to my family: my dad, Panka and Babi mama, who supported me during all of this despite the personal cost. I am grateful to Gabi for always making me feel at home. I would like to thank my aunts, Tünde and Noémi, for keeping the family together during difficult times. Végül, de a legfontosabb helyen, szeretném kifejezni hálám es szeretetem családomnak: apukámnak, Pankának és Babi mamának, akik mindigvégig támogattak személyes áldozatuk árán is. Köszönöm Gabinak, hogy hála neki, mindig otthon éreztem magam. Továbbá szeretném megköszönni nagynénéimnek, Tündének és Noéminek, hogy együtt tartották a családot a nehéz idökben is. The chances of finding out what’s really going on in the Universe are so remote, the only thing to do is hang the sense of it and keep yourself occupied. DOUGLAS ADAMS vii Contents List of Tablesx List of Figures xii 1 Introduction1 1.1 Galaxies.......................................2 1.1.1 Star formation...............................4 1.1.2 Active galaxies...............................6 1.1.3 Cosmic gas and dust............................ 10 1.1.4 Feedback processes............................. 12 1.1.5 Modelling approaches........................... 14 1.2 Observational signatures.............................. 15 1.2.1 Tracing star formation........................... 15 1.2.2 Tracing AGN activity............................ 21 1.3 Radio astronomy.................................. 23 1.3.1 Synchrotron radiation............................ 23 1.3.2 Radio interferometry............................ 24 1.3.3 Current and future radio interferometric surveys.............. 28 1.4 Summary...................................... 29 2 Further evidence for a quasar-driven jet impacting its neighbour galaxy 31 2.1 Introduction..................................... 32 2.1.1 Negative and positive feedback....................... 32 2.1.2 HE0450–2958 – a peculiar object with a history.............. 33 2.2 Observations and data reduction.......................... 35 2.2.1 Observations................................ 35 2.2.2 Calibration................................. 36 2.2.3 Imaging................................... 37 viii 2.3 Results........................................ 38 2.3.1 Single power-law synchrotron spectra..................